The present invention relates to an image reading apparatus in a scanner apparatus for reading an image on an original sheet, or a complex apparatus such as a facsimile, copier and the like, and more particularly, to improvements in a carriage support structure for scanning an original sheet image on a platen.
Generally, this type of image reading apparatus is widely known as an apparatus in which a light source emits light to an original document set on a platen, and the reflected light from the original document is guided to a photoelectric conversion means (for example, CCD) to electrically read, and is universally used as an input apparatus of a computer, input apparatus of a computer network, facsimile apparatus, copier, and complex apparatus thereof.
Conventionally, for example, as disclosed in Japanese Laid-Open Patent Publication No. 2004-72538 (Document 1), the apparatus is comprised of a platen to mount and set an original document, a light source for emitting light to the original document on the platen, a read optical system for guiding the reflected light from the original document to a photoelectric conversion means, and a photoelectric conversion element. Then, the read optical system is configured so that the light source lamp and reflecting mirrors are installed in a carriage moving along the platen at a predetermined velocity, the light source emits light to an original document on the platen, and that the reflected light is deflected by the mirrors to be guided to the photoelectric conversion means via a lens.
As such a read optical system, for example, as disclosed in Japanese Laid-Open Patent Publication No. H11-352603 (Document 2), a configuration is known that two, first and second, carriages are arranged to move along the platen, and that the light source and first mirror are disposed in the first carriage, while second and third mirrors for guiding the light from the first mirror are disposed in the second carrier. Then, the carriages are moved in the relative relationship so that the movement amount of the second carriage is one-half the movement amount of the first carriage. It is known that such a configuration enables movement strokes of the carriages to be set short, and thereby enables the apparatus to be compact and small.
In such a configuration, the first and second carriages are made of, for example, resin in the shape of a rectangle frame having a platen width (length in the sub-scanning direction), and are installed with the light source, mirrors and others. Then, the first and second carriages are mounted and supported on right and left paired guide rails disposed on opposite side portions of the platen, and configured to move at predetermined velocities by driving means such as a wire, belt or the like coupled to a driving motor. The guide rails are formed of metal material such as, for example, channel steel of U-shaped cross section, resin including, for example, flanges integrally formed with the apparatus housing, or the like.
When the carriages installed with the mirrors for guiding the light from the original document to the reading means as described above are moved along the document surface set on the platen, it is necessary to guarantee equilibrium characteristics (traveling stability) of the mirrors. In other words, for either of reasons that one of right and left paired guide rails is tilted up or down with respect to the platen surface formed in flat plane, the carriage itself is formed with distortion, and that the carriage is manufactured with wrong dimensional accuracy, a problem arises that a geometrical error occurs in an optical path extending from the mirror to the reading means (element).
Therefore, conventionally, the position and angular attitude of the mirror are configured to be adjusted (first adjustment) in installing the mirror in the carriage, and after building the carriage on the guide rails to be supported, the height position is adjusted (second adjustment) so that the carriage is fitted to the rail faces without rattling.
For example, it is proposed in Patent Document 2 described above that sliders are provided at four, front, back, right and left, places to reliably engage the second carriage, which guides the light from the first mirror installed in the first carriage to the reading means, in the right and left rail faces in mounting and supporting the carriage on the left and right guide rails, and that a height position of each of the sliders is configured to be adjustable. Although the adjustment procedure is not disclosed in the Document, the height position of each of the first to fourth sliders is adjusted after installing the carriage in the guide rails. In thus adjusting the positions of the sliders at four, front, back, right and left, places to accurately align the position and angular attitude of the mirror, the time and skilled work is required for the adjustments.
Meanwhile, it is generally known that a carriage is configured to contact the rail faces in three points when the carriage installed with the mirror is mounted and supported on the rail faces with flatness ensured. In such a configuration where the right and left side portions of the carriage are supported by three points, as described in Patent Document 2 as mentioned above, it is pointed out that the carriage swings vertically on the one-point support portion side, and that fluctuations in image and noise occur due to the vibration. Therefore, it is proposed in Document 2 that the sliders to engage the carriage in the rail faces are disposed at two front and back places on right and left rail faces, and that the height position of each of the sliders is adjusted independently.
However, when the carriage installed with the mirror undergoes a position adjustment on the rail faces with a height adjustment mechanism (such as adjustment screws, etc.), the following problem arises. The height adjustment requires for the slides at four places to be brought into contact with the rail faces with equal contact pressure, concurrently with adjusting the heights so as not to cause a gap between the slider of the carriage and rail face. The contact pressure adjustment requires complicated adjustment work, and causes the problem that the angular attitude of the mirror becomes misaligned during this adjustment.
For example, when one of right and left rail faces is inclined, or the carriage becomes distorted, the angular attitude of the mirror may be varied due to the above-mentioned height position adjustment. By the height position adjustment for fitting the right and left edge portions of the carriage along the rail faces, the angular attitude of the mirror installed in the carriage may become misaligned. For example, when the angular attitude of the mirror becomes misaligned from 45 degrees to 46 degrees, the reading start position of the original document on the plate becomes geometrically misaligned (the reading finish position is the same.)
Therefore, the inventor of the invention reached an idea of adopting a structure that right and left side edge portions of a mirror are supported by three points in supporting the mirror on the carriage, and adjusting a height position of the carriage on the side edge portion side for pivotably supporting by one point in accordance with the rail face. By this means, it is possible to obtain the adjustment mechanism that the mirror position and angular attitude do not become misaligned (do not change) largely even when an accuracy error such as tilt or the like occurs in the rail face or sliding surface of the carriage.
It is a principal object of the invention to provide an image reading apparatus for facilitating an optical adjustment of a mirror in supporting a carriage installed with the mirror on right and left rail faces to enable the carriage to move along a platen.